What kind of shape is it? Is it more on the circular side or is it more of a rectangle or kidney shape? I vote Florida natives, but the exact stock would come down to the actual dimensions.
If it's got a reasonable amount of surface area and is at least 180 gallons or so, then I'd say look into getting a Florida gar. They're really cool primitive fish and would look great in a pond. They don't get terribly large (under 24") and can be trained to accept pellets and prepared foods instead of feeders. I used to have one, and I hand fed it pieces of fish fillet; it enjoyed being pet and was kind of like a puppy!
If you're more into smaller fish (or have insufficient room for a gar), then go with the previously mentioned fish such as flagfish.
If it's got a reasonable amount of surface area and is at least 180 gallons or so, then I'd say look into getting a Florida gar. They're really cool primitive fish and would look great in a pond. They don't get terribly large (under 24") and can be trained to accept pellets and prepared foods instead of feeders. I used to have one, and I hand fed it pieces of fish fillet; it enjoyed being pet and was kind of like a puppy!
If you're more into smaller fish (or have insufficient room for a gar), then go with the previously mentioned fish such as flagfish.